Cryopumps currently available are typically used in equipment for the manufacture of integrated circuits and other electronic components, as well as for the deposition of thin films in a variety of consumer and industrial products. The utility of the cryopumps is to create a contaminant-free vacuum by freezing or pumping out gases in a work environment.
The design concept of these cryopumps are similar. The cryopumps comprise a low temperature surface called a primary pumping surface, which operates in the temperature range of 4 to 25K and a higher temperature surface, which operates in the temperature range of 70 to 130K. The higher temperature surface, often called a radiation shield, surrounds the primary pumping surface and provides radiation shielding and a pumping site for the higher boiling point gases. The spacing between the primary pumping surface and the radiation shield must be sufficient to permit unobstructed flow of low boiling temperature gases from a vacuum chamber to the primary pumping surface. Between the chamber to be evacuated and the low temperature surfaces is a frontal array, which also serves as a radiation shield for the primary pumping surface. The frontal array is typically cooled to 110 to 130K by thermally coupling it to the radiation shield.
In operation, high boiling point gases, such as water vapor, are condensed on the frontal array. Lower boiling point gases pass through that array and into a volume within the radiation shielding where they condense on the primary condensing surface. Often, an adsorbent, such as charcoal, is placed adjacent to, but shielded by, the primary condensing surface and is operated at the temperature of that surface to adsorb gases which have very low boiling point temperatures and are not condensed on the primary surface. With the gases thus condensed and/or adsorbed onto the pumping surfaces, only a vacuum remains.
The refrigerator used for cooling the pumping or adsorbent surfaces may be an open or closed cycled cryogenic refrigerator. The most common refrigerator used is a two-stage cold-finger, closed-cycle refrigerator. Typically, the cold end of the second stage, which is the coldest stage, is connected to the primary pumping surface. The first stage is connected to the radiation shield which surrounds the primary pumping surface.